The present invention relates to methods and apparatus for detection and treatment of the disease process known as myocardial ischemia and/or infarction (MI/I).
Ischemia occurs when the blood supply to the heart muscle is temporarily or permanently reduced, such as may result from the occlusion of a coronary artery. This occlusion may lead to local ischemia or infarction of the heart muscle. Ischemia may also occur over large sections of the heart muscle due to conditions such as cardiac arrest, heart failure, or a variety of arrhythmias. The ischemic event can be of the so called xe2x80x9csilent typexe2x80x9d described in medical literature (e.g. not manifesting itself in terms of symptoms experience by the patient or obvious external indications). The event can also be chronic with continuously evolving symptoms and severity due to underlying heart disease, or very abrupt and possibly even fatal due to infarction of large enough area of the heart to cause a large myocardial infarction.
The ischemic event often causes the performance of the heart to be impaired and consequently manifests itself through changes in the electrical (e.g. the electrocardiogram signal), functional (e.g pressure, flow, etc.) or metabolic (e.g. blood or tissue oxygen, pH, etc.) parameters of the cardiac function.
The conventional approach to detection of MI/I is to analyze the electrocardiogram (ECG). An ischemic event results in changes in the electrophysiological properties of the heart muscle that eventually manifest themselves as changes in the ECG signal. The current state of the art is to record these ECG signals from the body surface using amplifiers and associated instrumentation. A standardized set of electrodes in an arrangement known as a 12-lead ECG has been developed. The conventional approach to the detection of ischemia and infarction relies on analysis and interpretation of characteristic features of the ECG signal such as the ST-segment, the T-wave or the Q-wave. Computer-based technology has been employed to monitor, display, and semi-automatically or automatically analyze the ischemic ECG changes described above. The present technology includes ECG machines used in doctor""s office, portable ECG machines known has Holter recorders, bedside monitors with displays, and sophisticated computer-based system for automatic analysis of the ECG signals.
Technology exists for providing therapy once ischemia is detected. The most common approach involves thrombolytic therapy (by external infusion of drugs such as TPA or streptokinase) or opening of the blocked vessels using a variety of angioplasty catheter devices. In the event that ischemic condition results in malignant arrhythmia or arrest of the heart, an external defibrillator may be used to shock the heart and restore the cardiac rhythm.
Technology also exists for implanting therapeutic devices for treating electrical conduction disturbances or arrhythmias of the heart. These devices include implantable pacemakers, cardioverters and atrial and ventricular defibrillators, drug infusion pumps as well as cardiac assist devices. The implantable devices typically use intracavitary leads to sense the electrogram (EGM) and then provide electrical therapy (pacing or defibrillation) or mechanical therapy (pumping blood). These devices sense the EGM and then utilize the features, such as improper conduction (in case of a pacemaker) or a fatal rhythm (in case of a defibrillator), or simply timing (to coordinate mechanical pumping). Notably, these devices do not specialize in the task of detecting, alerting the patient or treating ischemic heart disease.
Ischemia detection and analyses are usually done manually by the expert cardiologist or by computers employing algorithms to detect ischemia-related changes in the ECG signals. The preferred features of the ischemia detecting computer algorithms are the ST-segment and the T-wave. These features show elevation, depression or inversion of these ECG signals associated with ischemia. The computer then carries out a careful measurement of the degree of elevation/depression in a specific lead. By identifying ischemia dependent changes from specific leads, the ischemic event is attributed to a specific region of the heart.
The current approach to diagnosis is that after an ischemic event is perceived by the patient, they contact medical personnel such as the xe2x80x9c911xe2x80x9d system or their personal physician. Within the clinical setting, the patient is often monitored using a short recording of the ECG signal which may be interpreted by a physician. Alternately, the high risk patient may be continuously monitored at the bedside in a cardiac intensive care unit. Therapy may include using drugs such as TPA, use of catheters for angioplasty (opening the blocked coronary vessel using a balloon or laser), or providing life support back up such as defibrillation.
The aforementioned cardiovascular medical monitoring technology and medical practice have several significant drawbacks in regard to the detection and treatment of coronary ischemia which can result in severe consequences to the patient up to and including death. They include the following:
1) Not being able to immediately alert the patient and/or the physician of an ischemic event, particularly a life threatening event.
2) Not being ambulatory with the patient; and/or an inability to provide continuous monitoring to the patient and indication of the necessary diagnostic information to the physician.
3) Requiring input and interpretation of a physician or medical practitioner when one may not be present.
4) Requiring monitoring devices external to the body, such as an ECG monitor or external defibrillator, which are usually only available in medical centers and hospitals, and which further need special expertise and attention from medical personnel.
5) Reduced sensitivity or otherwise inability to detect ischemic events due to loss of sensitivity from use of external electrodes.
6) Loss of specificity as to the site of ischemia due to inadequate placement of electrodes in the vicinity of the ischemia or infarction.
7) Needing sophisticated expertise of a cardiologist to interpret the clinical condition or needing monitoring instruments with sophisticated computer-aided ECG signal analysis capabilities.
8) Over reliance on use of ECG signals for detection and inability to utilize and integrate other physiological data, (e,g pressure, blood flow, and PO2).
9) Inability to immediately alert the patient or the physician of the impending or emerging ischemic condition.
10) Inability to provide immediate treatment, particularly for life-threatening events (e.g. myocardial infarction, cardiac arrest).
Certain embodiments of the present invention relate to methods and devices for detection of myocardial ischemia and/or infarction (MI/I). Preferred embodiments relate to electrodes and sensors, devices and methods for interpreting ischemic conditions, devices and methods for initiating the procedure to alert the patient and/or the care-giver, and devices and methods for connecting with a device that provides therapy. MI/I may be detected using implantable devices and methods according to certain embodiments of the present invention.
Embodiments may include a stand alone device or a modification of another implantable device such as a pacemaker, cardioverter, defibrillator, drug delivery pump or an assist device. Embodiments may use a variety of in vivo sensors located inside the human torso and/or inside the heart. The sensor device preferably includes electrodes that are indwelling in the heart, on or in the vicinity of the heart, under the skin, under the musculature, implanted in the thoracic or abdominal cavity. Preferably the sensor device also includes strategic placement of the electrodes to capture the EGM signal from various positions and orientations with respect to the heart. The sensor device also preferably includes other hemodynamic or mechanical sensors that are sensitive to the condition of the heart in MI/I. MI/I may be recognized using analysis of the features of the signal, namely the EGM, recorded by the electrodes and sensors. The features of the EGM signal (namely, depolarization and repolarization), morphology, and analytical information such as the spectrum, wavelet transform, time-frequency distribution and others, are utilized in the interpretation and recognition of the MI/I condition. Separately or in conjunction, the hemodynamic (namely, blood pO2, pH, conductance, etc.) and mechanical parameters (blood pressure, blood flow, etc.) are sensed according to the embodiments of this invention. MI/I is then recognized by integrating some or all of the sensor information. Embodiments may detect this MI/I event and alert the patient using a variety of methods, including but not limited to vibration, electrical stimulation, auditory feedback, and telemetry. The device to alert the patient may in certain embodiments be incorporated within the instrument itself. The patient may be alerted by direct communication via electrical, sound, vibration or other means or indirect communication to an external device in an electromagnetic link with the implanted device. Once the MI/I event is identified, the device may also institute therapy, such as infusion of a thrombolytic agent or delivering life saving shock in case of an arrest, semi-automatically or automatically. The therapy giving device may be integrated with the MI/I detection, MI/I analysis, and/or patient alerting device into an integrated or separate stand alone system.
Embodiments of the invention may be used to detect MI/I from inside the body as compared with the traditional approach of detection by placing electrodes on the outer body surface of the torso. This is made feasible in certain embodiments by using the MI/I detection technology in an implantable device. Embodiments utilize sensors, such as electrodes and leads, that record the EGM signal from inside the chest in the vicinity of the heart and/or from electrodes placed on the heart, and/or using catheters or leads placed inside the cavities (atria and ventricles). Embodiments may include built-in interfaces to electrodes, namely circuits for amplification and filtering of the signals, and the circuit for digitization (analog-to-digital conversion) and processing (microprocessor). Embodiments of the implantable device, using its microprocessor, analyze the features of the EGM signal from these leads to detect an ischemic event.
Embodiments also relate to the design, construction and placement of electrode sensors. Embodiments may include an electrode lead with multiple sensors capable of recording EGM from multiple, strategic locations in the chest or in and around the heart. This embodiment also includes utilization of the body of the instrument and single or multiple leads.
Embodiments also relate to detection of the ischemic event including identifying particular features of the EGM signal. These features include depolarization (i.e. initial excitation of the heart when a beat is initiated, coincident with the body surface QRS complex) and repolarization (i.e. the subsequent repolarization of the heart coincident with the body surface ST-segment and T-wave). MI/I results in alteration in depolarization and repolarization waves in selected regions of the heart, for the case of focal ischemia, or the entire heart, for the case of global ischemia. These changes alter the action potential (of heart cells) as well as the conduction pattern (in selected regions or the whole heart). The alterations in action potential shape and conduction change together alter both the depolarization features as well as the repolarization features). Depending on where an electrode is placed, these features may be seen in different recordings. The electrodes pick up the local signal (from the heart muscle in its vicinity) as well as the distal signal (distal muscle areas as well as the whole heart). The characteristics of this signal are identified in the form of shape changes, and these shape changes can be identified in a variety of ways, including temporal, spectral, and combined approaches.
The MI/I detection technology according to embodiments of the present invention, may also utilize non-electrical measures, including hemodynamic and mechanical parameters. An MI/I event may result in a degree of deprivation of oxygen to the heart muscle. This in turn may result in a decreased ability to perfuse the heart muscle as well as the body. This may result in a cyclical reduction in the mechanical performance in terms of contractility and pumping action of the heart. Sensors placed inside the blood stream pick up the changes in blood oxygen, pH, conductance, etc. resulting from the MI/I event. The MI/I event would lead to small changes in case of mild ischemia or infarct or significant changes in case of global ischemia or cardiac arrest. The sensors are usually placed inside a catheter or a lead, although some times in the body of the instrument, and then measurements may be made via the electronic circuit interfaces inside the implantable device. The mechanical function of the heart may be detected utilizing sensors and leads, including those for pressure, volume, movement, contractility, and flow.
Embodiments also relate to methods and devices for signaling the host patient or others (such as medical personnel) to the incidence of MI/I. When MI/I is detected, it is imperative to take therapeutic actions rapidly and even immediately. Thus, the patient needs to be informed and the caregiver physician needs to be informed. Embodiments of the invention include devices and methods for communication between the implantable device and the host/physician. One of these approaches is to use radio-frequency or radiotelemetry, while another is to communicate through electrical stimulation. Other approaches, including sound, and magnetic fields are also devised. Embodiments may also utilize long distance, remote and wireless means of communication using telephone, telemetry, Internet and other communication schemes. Embodiments may also include the code of communication by which the information pertinent to MI/I is presented in detail. This code may be either analog or digital, relayed via the communication link, and then decoded by the receiving instrument or individual. The code primarily signals to the host patient, or the external device attached to the patient, or directly to the medical caregiver, the condition of MI/I. The code may include information about EGM, the MI/I condition, and other related diagnostic information. The code may also include recommendation and instructions to provide an immediate therapy to the patient to treat MI/I.
Another aspect of certain embodiments of the invention includes coupling of the MI/I detection technology to a variety of therapeutic devices. The implantable MI/I detection technology makes it feasible to rapidly initiate therapy through direct access to the body, circulatory system or the heart. In some circumstances it is desirable to infuse drug such as Streptokinase or TPA to treat the patient. Other drugs may also be infused immediately or subsequently on a steady state basis. In other instances it is desirable to carry out procedures such as angioplasty. In case the MI/I event leads to a life-threatening arrhythmia or cardiac arrest, means to treat the arrhythmias to resuscitate the heart are disclosed. These may include use of electrical pacing, cardioversion and/or defibrillation. In case the MI/I event leads to a failure of the heart, means to assist the heart are disclosed. These assistive devices include left or right ventricular assistive device and artificial heart pump. Embodiments may declare interface of the implantable myocardial ischemia detection technology to these therapeutic approaches and the use of these therapies upon discovery of MI/I by the implanted devices.
Another aspect of certain embodiments of the invention includes the use of the technology in an implantable device. The implantable device may include a hermetically sealed can, electronics, analog and digital logic, microprocessor, power source, leads and sensors, circuits and devices to alert the patient, communication link and interface to the external diagnostic and therapeutic means. Embodiments also include modification of implantable arrhythmia detection devices, pacemakers, defibrillators, infusion pumps, or assist devices to have the novel features described above. The technology used in embodiments of the present invention can be partially or fully integrated into these instruments. Embodiments further include hardware, software or firmware modification of the aforementioned devices to have MI/I detection, alerting and therapy initiating features.